The essential components of a conventional chocolate formulation are cocoa "nib", i.e. the roasted cocoa bean with shell and germ removed, sugar and cocoa butter additional to that contained in the nib. Cocoa nib is approximately 55% cocoa butter, the balance being proteins, carbohydrates, tannins, acids etc. The cocoa butter content of the chocolate controls its setting characteristics and largely governs its cost, and while the ratio of cocoa nib to sugar determines the type of chocolate, the cocoa butter content varies according to the application. Thus, bitter sweet chocolate has a ratio of nib to sugar of 2:1 while sweet chocolate has a ratio of 1:2. Moulding chocolate may have a fat content of 32%, covering chocolate 33 to 36%, chocolate for hollow goods 38 to 40% and chocolate for covering ice-cream 50 to 60%.
The typical preparation of chocolate involves four stages. In the first stage the ingredients are mixed together in a process which also involves grinding or rubbing e.g. on a multiple roll press to provide a smooth fluid paste. The ingredients may be added sequentially and in particular the cocoa butter may be added step-wise to control the viscosity of the composition. The sugar may also be pre-ground to a smaller particle size to reduce the length of time required in the grinding/rubbing of the chocolate mixture. Most chocolate, and certainly all good quality product, is subjected after mixing to the process of "conching" in which the chocolate mixture is subjected to mechanical working to give the chocolate a fuller and more homogeneous flavour. Other ingredients such as flavours e.g. vanilla and extra cocoa butter may be added at this stage if desired. A frequently added additional ingredient is lecithin or other emulsifier which improves the flow properties of the chocolate and thereby enables the amount of cocoa butter to be reduced. The third stage of the chocolate preparation is called "tempering" in which nuclei are provided in the liquid chocolate composition to facilitate the rapid crystallisation of its fat content on cooling. The final appearance of the chocolate, its texture and keeping properties depend upon correct tempering stage conditions. After tempering, the chocolate may finally be cast into moulds to set or may be used in an enrobing process to produce chocolate coated confectionery etc.
The present invention is concerned in particular with the conching step in the process described in the preceding paragraph. The changes taking place during conching are subtle and not completely understood. What is certain is that the texture of the chocolate is improved and the flavour changed to the extent that without conching the taste of the chocolate is generally commercially unacceptable. The kneading action during the conching process and the maintenance of an elevated temperature together cause evaporation of moisture and volatile acids such as acetic acid, destroy harsh flavours and reduce astringency, probably due to modification of tannins. There are two types of conching operation called, "dry" conching and "wet" conching. In wet conching all of the cocoa butter and other ingredients such as lecithin are added early in the process to maintain the fluidity of the mass which is then mechanically worked for a prolonged time e.g. 20 or 30 hours or more and at a relatively low temperature e.g. 40.degree. C. up to 60.degree. C. The dry conching process on the other hand is operated for a shorter time e.g. up to 20 hours but at a higher temperature e.g. above 60.degree. C. and usually about 80.degree. C. and in this case the extra cocoa butter and other ingredients are added towards to the end of the conching period e.g. about one hour before the end of the period.
The conventional chocolate composition uses sucrose as sweetener but many other sweeteners have been proposed and some have been used to provide for example dietary type chocolate for diabetics, and slimmers. One class of replacement sweetener for sucrose in chocolate is the so-called sugar alcohols in particular sorbitol, maltitol and mixtures of sugar alcohols known as hydrogenated starch hydrolysates. Sugar alcohol sweeteners, besides contributing fewer calories to the chocolate than the equivalent quantity of sucrose are also far less cariogenic. The disadvantages of using sugar alcohol sweeteners is that in general it is only possible to carry out the conching of the chocolate composition at temperatures below 55.degree. C. and for sorbitol in particular the temperature must not rise above 40.degree. C. Thus, in the publication of the paper entitled "Zuckerfreie Pralinen--Zuckerfreie Fuungen und Schokolademassen" presented at the International Conference "Inter-Praline 87' in June 1987 at the Zentralfachschule der Deutschen Susswarenwirtschaft, Solingen it is reported that at temperatures above 40.degree. C. conching of chocolate containing sorbitol leads to agglomeration of the mixture and in two compositions containing maltitol and xylitol the conching is carried out at 35.degree. to 38.degree. C. Similarly, in chapter 4 of "Developments in Sweeteners -3" entitled "MALBIT and its applications in the Food Industry" on page 95 the conching temperatures for chocolate compositions containing maltitol are given as 46.degree. C.
The experience of the chocolate industry is that the relatively low temperatures required for the conching of chocolate compositions containing sugar alcohol sweeteners necessitates wet conching for a very long conching time e.g. up to 24 hours and even then the flavour development is not as satisfactory as when a higher conching temperature is possible. We have now found however that there are two sugar alcohols which can be used as part or all of the chocolate sweetener and which permit the composition to be dry conched at an elevated temperature. These sugar alcohols are erythritol and maltitol with the proviso that the maltitol must be more than 90% pure. Erythritol is a symmetrical molecule and is therefore normally available as the meso-form. References to erythritol in the remainder of this specification and in the claims will mean the meso-form.